Fluorescence changes will be used to detect the temperature-jump relaxation processes corresponding to binding of the carcinogen 4- nitroquinoline-N-oxide (4-NQO) to uncharged transfer RNA (tRNA) from yeast and rat liver. From these kinetic studies the mechanisms of binding should be derivable, and can be compared with earlier studies of ethidium- and proflavine-tRNA interaction. Fluorescence polarization and induced circular dichroism measurements may also be performed to aid in defining the nature of the 4-NQO/tRNA complex. The effect of 4-NQO binding to tRNA upon the reaction of the latter with elongation factor I (EF I or EF Tu) of protein synthesis will be examined using highly purified elongation factors from E. coli and rat liver. Possible effects of high macromolecule concentration on tRNA conformation (the psi transition), particularly as this may influence ligand-binding, will be further studied. Other planar aromatic carcinogens such as benzacridines will be tested for possible interaction with tRNA. The kinetics of 3,4-benzpyrene-DNA binding will be investigated using the temperature-jump technique with fluorescence detection.